so i came across this planned NASA drone and thought, wouldn't it be cool to make something like that for earth

im planning to make a autonomous quadcopter drone that has a GPS and can communicate with a raspberry pi, the raspberry pi will have 3G cellular modem with witch it can receive commands
and send photos (maybe even a video feed) back. the idea is that the drone can travel long distances in short hops and gather data/photos along the way
to recharge its battery's it will need to have solar panels. im aiming for one hop every 7 days (with optimal sun) and a range of 3 - 5 Km for a hop
here is my current layout

im going for 4 x 2.5 W solar cells that give about 6V each. im going to have two sets of two in series to get 12 V to charge 2 x 2cell lipo battery's
i also have a separate battery for the raspberry and other 5V electronics
to conserve energy during charging i am planning to cut off most of the electronics from the power supply and only turn parts of the electronics on when needed
im also looking into a sleeping circuit to completely turn off the raspberry during the night or cloudy days.
here is a rough draft (im only going to CAD when i have all components working)

the camera will be used to take pictures when landed and looking down in flight
i have build drones before so that wont be a problem. the raspberry isn't that hard either. but i have little experience with lipo charging.
because this system will be on its own for long periods of time i want to use a balanced 2S charger, this seems to be a really rare thing
im really struggling to find the best configuration here. the main requirement of this BMS is that its efficient and reliable
here are some questions that i still need to figure out
-will it be more efficient to have a Boost Converter between the solar panels and the charger
-what is the best configuration of the solar panels/battery
-what motor/propeller works efficient at the chosen battery configuration
-how to weather-proof the brush less motors
any input would be greatly appreciated
this i just a hobby project so i am trying to keep it under 1000$
i have a 3D printer that i will use to print the frame, i am currently testing out chargers with the solar panels